Transdermal delivery of drugs, that is, delivery of drugs through the skin, provides many advantages. The method is a comfortable, convenient, and noninvasive way of administering drugs. Many of the variables and side effects associated with oral administration are eliminated. Since the early 1970s, there has been substantial effort spent on developing particular systems for effectively delivering drugs in a transdermal mode. A variety of devices containing, at minimum, a drug reservoir and a backing, and optionally containing other layers, such as an adhesive layer for adhering the device to the patient, a drug release rate controlling layer for moderating delivery rate, and the like, have been constructed. With certain drugs, in particular scopolamine and nitroglycerine, it is feasible to construct a transdermal drug delivery device which will achieve therapeutically effective levels of the drug in the patient. Commercial products have been introduced to deliver these two materials. However, one of the key problems with transdermal administration of many other drugs has been the low penetration or permeation rate of drug through the skin of the patient. The research over the past two decades has identified various skin permeation enhancers. These materials increase the rate of penetration of drugs across the skin.
Typical enhancers in the art include ethanol, glycerol monolaurate, PGML (polyethylene glycol monolaurate), dimethylsulfoxide, and the like. Many highly attractive drugs, such as estradiol, progestins and the like are commonly formulated with enhancers for transdermal delivery.
The use of permeation enhancers is not without its drawbacks. For one, the permeation enhancer typically is coadministered with the desired drug. That is, the permeation enhancer passes through the patient's skin at the same time the drug does. Depending upon the exact nature of the permeation enhancer, this can lead to side effects related directly to the permeation enhancers.
Another disadvantage is that the enhancers are often organic solvents, which can in some cases react with and alter the character of the drug being delivered. In addition, the enhancers can interact with the patient's skin, in some cases causing irritation and the like. Moreover, enhancers can interfere with the mechanical properties of the devices, such as interfering with the effectiveness of adhesive layers and the like.
The present invention provides drug-matrix constructions which, when contacted with patient skin, allow high rates of delivery of drug without the necessity of added permeation enhancers previously required to reach therapeutic blood levels.